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Q.

The pistons in the front brake calipers on my 1994 Discovery 1 V8 hold the pads right against the disc, and although they’re not seized on (I can turn the wheels by hand) the brakes quickly get hot, which makes them squeal.

I’ve replaced various components such as flexi hoses (now Goodridge braided) and the master cylinder (brand-new), as advised by various mechanics – including those at my local Land Rover service centre. But it’s all been to no avail.

A while back, after having problems with corroded pistons, I decided that stainless pistons with new seals would provide a permanent solution. The question now, however, is whether I installed them correctly. Is there a right and wrong way to fit the seals?

I’m told the seals are tapered, but I couldn’t see a taper on a new set at the service centre. Is the taper machined into the recess in the caliper? If so, does it matter which way the seal goes in? Also, can the dust seals cause the pistons not to pull back?

Craig Lowther, West Yorkshire

A.

Assuming there was no corrosion, wear or scoring inside the caliper bores, the new pistons and seals should work correctly. The piston seals are not tapered, but have a rectangular profile, so they can only be fitted the correct way around. The dust seals shouldn’t restrict the pistons’ movement.

The seals pull the pistons back slightly after the pedal is released, but only enough to relieve the pad pressure on the disc. The pads will still be positioned next to the disc and may contact it slightly when the disc is spun by hand, but not enough to cause any significant restriction. If you can still turn the wheel freely by hand after applying the foot brake, this suggests that both the pistons and seals are okay.

The brakes will become very hot with only a small application. To reduce the squeal you could try re-cleaning the piston edges that touch the pads, and also the back of the pads, then smear copper grease lightly in this contact area, ensuring it doesn’t get on to the friction faces.

Alternatively, if your pads don’t have a slight chamfer on their leading edges (the edge the rotating disc contacts first) try filing a light chamfer along this edge on each pad. Also ensure the upper and lower seats where the pad fits into the caliper are clean and smooth to allow slight free movement of the pad.

In the case of Discovery 2 brakes, check the caliper carrier is free to move on its guide pins. The pins may need cleaning and regreasing, or renewing if worn.

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